The present invention relates to a pest control chemical for controlling pine wood nematodes (Bursaohelenchus xylophilus Mamiya and Kiyohara), and particularly to a repellent and a nematicide against the pine wood nematodes comprising a substance contained in pine trees such as Formosan masson pines (Pinus massoniana Lamb), Eastern white pines (Pinus strobus L.) and Longleaf pines (Pinus palustris Mill.), to a nematicide against pine wood nematodes containing a hydroxystilbene, and to a method for synthesizing hydroxystilbenes.
As well known, the pine wood nematode, fungivorous nematode, enters pine wood tissues and propagate to cause the pine trees to die.
The mechanism by which the pine wood nematodes cause the pine trees to die is considered as follows:
a) In the pine trees infected with the pine wood nematodes are produced toxins (phytoalexins) such as benzoic acid (1), catechol (2), dihydroconiferyl alcohol (3), 8-hydroxycarvotanacetone (4) and 10-hydroxyverbenone (5), PA1 b) The nematodes secrete cellulase, PA1 c) Tracheids of the pine trees are clogged with .alpha.-pinene and .beta.-pinene abnormally accumulated after the nematode infection, and PA1 d) Toxins are secreted by molds which propagate in the pine trees after the nematode infection. PA1 (1) A great deal of labor is required. PA1 (2) It is difficult to decide the suitable time of insecticide application because the time of eclosion and escape of the pine sawyers differs from year to year. PA1 (3) The effectiveness of the insecticides has become lowered. PA1 (4) In order to achieve the exterminating effect in forests and fields, the dosage per unit area is required to be 10 times that generally used in agriculture. PA1 (5) Social problems such as the remaining of the given insecticides in soil, the remaining in water systems and the effect on ecosystems such as surrounding animals and plants are encountered. PA1 (6) The previous synthetic nematicides for directly exterminating the pine wood nematodes in wood are effective, but have a problem in safety because of their toxicity.
The pine wood nematodes are transmitted to the pine trees through injurious insects such as a pine sawyer (Monochamus alternatus Hope).
Previous methods for preventing pine trees from dying by the pine wood nematodes mainly include (1) Cutting down damaged trees to exterminate ova, pupae and adults present in the damaged trees before the pine sawyers carrying nematodes, which are directly responsible for the death of the pine trees, escape from the damaged trees, and (2) the insecticide applications (sprinkling and cropdusting) for preventing maturing feeding after eclosion and escape of the pine sawyers. The insecticides used herein include organic phosphorus pesticides, NAC agents (1-naphthyl-N-methylcarbamate), PAP agents (ethyl dimethyl-dithiophosphorylphenylacetate), EDB agents (1,2-dibromoethyl), MPP agents (0,0-dimethyl-0-[3-methyl-4-(methylthio)phenyl]thiophosphate) and MEP agents (dimethyl(3-methyl-4-nitrophenyl) thiophosphate).
In addition to the above-mentioned insecticides for the pine sawyers, nematicides for directly exterminating the pine wood nematodes in pine trees include a levamisole hydrochloride agent containing levamisole hydrochloride as a main insecticidal ingredient (trade name: "Century", Mitsubishi Petrochemical Co. LTD., Japan), a mesulfenfos agent (trade name: "Nemanon", Nihon Bayer Agro Chem. K/K, Japan) and a morantel tartarate agent (trade name: "Greenguard", Fizer Pharmaceutical INC., Japan).
The previous methods for exterminating the pine sawyers have the following problems:
The sufficient controlling effect can not be attained because of these problems.
It has hitherto be unknown at all that an extract from a pine tree with an organic solvent, an extracted compound or hydroxystilbenes is effective as a pest control chemical for controlling the pine wood nematodes.